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  1. #1

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    I own a 1970 Bronco that the previous owner put disk brakes on (dana 30 front). I have a few questions.

    1) I am used to driving a 97 grand cherokee with disks all the way around, so I may not be calibrated to how an old 1970 Bronco is supposed to feel when you stomp on the brakes....I don't expect to stop on a dime, but what should this steed feel like when I pull the reigns?

    2) What types of problems arise when swapping disk brakes on an early bronco dana 30? The proportioning valve is stock 1970, the master cylinder is the larger chevy master cylinder.

    Anything helps,
    Chris

  2. #2
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    Obviously, it'll never stop like a vehicle equipped with ABS. You need to get the proper proportioning between the front discs and rear drums in order to stop the best. EBs didn't have front discs in '70, so I'm not sure what you mean by a stock 1970 proportioning valve. What's it out of? I'd also check the master cylinder, it may have an internal proportioning valve if it's for a disc brake application. You don't want two proportioning valves in the system.

    EBs are heavy, and with off road tires, they'll never stop like something newer.

  3. #3

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    Stupid question, but are we talking power brakes or manual brakes? Even with a properly setup brake system an EB is diffucult at best to stop without power brakes. If you do have power brakes it may be a proportioning valve issue. Hit a gravel road see what locks up first, then look into how the valves are setup as mentioned above.
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  4. #4

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    Stupid question, but are you sure its a 30? The usual suspect for a disc brake swap is a Dana 44. I think those came in in 70 1/2 model years and up.

    Can you lock the brakes up? If you can, it might just be that you are used to the newer model and everything is ok. If you can't lock 'em up then you need to look at things. If the rears lock but the fronts don't then you need to adjust the master cylider. I have heard that late 70's F-250 master cylinder's work well.

    Contact Bsaunders on this board. He runs his own Classic Bronco supply business and knows his stuff on them.

    phyler
    <a href="http://www.nbwheeling.org" target="_blank">www.nbwheeling.org</a>

  5. #5

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    I would guess that it being a stock 1970, that the brakes are manual (no booster). My 72 has manual drums all around and I can lock up all four with my 36 inch tires. It just takes alot of leg power. If you are used to driving powered disks, getting the hang of standing on the brake pedal every time takes some getting used to.

    The 70 should have a Dana 30 front, ID the axle here , but I have never yet heard of putting disks on a 30, usually on a 44. I guess it can be done though.

    If it is simply a dislike of the manual braking system, you can put vacuum booster system on it, there are many suppliers for kits. Or if mechanically oriented, put on hydroboost brakes.

  6. #6
    imported_david
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    Originally posted by csangster:
    I own a 1970 Bronco that the previous owner put disk brakes on (dana 30 front). I have a few questions. SEE BELOW

    1) I am used to driving a 97 grand cherokee with disks all the way around, so I may not be calibrated to how an old 1970 Bronco is supposed to feel when you stomp on the brakes....I don't expect to stop on a dime, but what should this steed feel like when I pull the reigns?
    I run the chevy disks in the front and mine grab really good they do not lock it up! BUT it does bring it to a pretty quick stop, and will droop the front end.

    2) What types of problems arise when swapping disk brakes on an early bronco dana 30? NONE IF IT WAS DONE RIGHT! The proportioning valve is stock 1970, the master cylinder is the larger chevy master cylinder.
    The chevy disk swap is the way most people go, and yes you can put this on a dana 30. you say you are running the "stock" proportioning valve. is the master cylinder set up for disk \drum? if so the stock valve could be wrong, it needs to match the presure the master cylinder is sending to the brakes.
    check out www.classicbroncos.com or the every dreaded pirate board under FORD or www.bronco.com and go to tech or join that e-mail list and ask the question there.

    Anything helps,
    Chris

  7. #7

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    Thanks for the input,

    I just subscribed to classicbronco.com forums and will use them for some additional technical assistance.

    Another question: The valve downstream of the master cylinder that directs fluid to the front and rear brakes; is the stock unit on a 1970 a propotioning valve or not?

    Like I said earlier, I installed a chevy master cylinder to remedy the situation, but I wonder if it wasn't the problem.

    I have a set of 1976 axles that I will eventually put under the bronco, but I want to make sure this brake setup works well first. And hopefully I won't have to fuss with the master cylinder/pro valve any more.

    thanks again,
    Chris

  8. #8

    Post

    Okay,

    Here is an update on my early bronco disk brake problem.

    I took her out for a spin and slammed on the brakes and, far as I could tell the rears locked up first. I came back and felt the front disks and they WERE hot, so I know the front brakes are being actuated to a certain degree.

    Are there any other ways to test the system to make sure that I am getting the proper bias in brake pressure?

    Thanks,
    Chris

  9. #9
    imported_david
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    Chris,
    I will take another stab at this, you have a 70 Eb with Disk front. You used the 70 Proportioning valve set up for drum rear\ drum front. problem one.
    question two are your brakes power assit? or are they manuual still?
    If power, chances are the valve needs to be changed to send more fluid to the front. plus your master cylinder may be wrong here also.
    if they are not power assit go back to the stock EB master cylinder and pull the resduial (sp) valve out of the front brake side. and keep your stock proportioning valve.
    or # 3 pull the proportioning valve and get some adjustable valves from willwood, summit, jegs etc. not sure who has them in denver.and dial in your settings where you need them.

  10. #10

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    Quite a few of the orginal "proportioning" valves are really only safety valves that block the front or back port in case of loss of pressure due to a broken line. The later '76-'77 meter blocks are actual proportioning valves, but for a fraction of the cost you can get a wilwood proportioing valve and dial it in yourself. Since ~70% of your braking (on the street) is done by your front brakes, you want to set up the system so the rear locks up only slightly before the front.
    If you are using a master cylinder for drum drum you do need to remove the residual pressure valve for the front line or you are going to drag your disc brakes constantly. This will result in much shorter brake life and less effective brakes as they will much hotter than normal.

    (disclaimer - I am not a brake tech, nor am I a certified mechanic. Please work on your brake system with full knowledge of what you are doing or take it to a professional who does.)
    -Ben
    74 Bronco garage queen - currently a zero emission vehicle
    my commuter vehicle spews "global warming" gas CO2 & CH4 - dang bicycles

  11. #11

    Post

    If I understand what you are describing, it is not a proportioning valve, rather an imbalance switch. It activates the warning light on the dash of the EB (right below the ignition keyset). More info about it is HERE

    When you swapped to disks, the front brakes using calipers have different volume/pressure needs. A drum brake has a narrow long throw cylinder while the disk caliper has a wide short throw cylinder. Typically the drum cylinder requires high pressure and low volume to actuate while the caliper needs higher volume and lower pressure. This is confused further with the need for additional braking force at the front axle as the weight of the vehicle ends up on that axle when you apply the brakes (what bsaunder was saying).

    Changing the master cylinder can help if it is set up properly for the brake system you are using. Generally when aftermarket brake systems are installed the easiest way to balance the brakes for use on the street is with a proportioning valve. They are relatively cheap and easy to install. Then the balance is achieved through trial and error by adjusting the valve and trying the brakes until you get the stopping effect that you want.

    Good luck.

    Oh yeah
    (disclaimer - I am not a brake tech, nor am I a certified mechanic. Please work on your brake system with full knowledge of what you are doing or take it to a professional who does.)

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